A moral doctrine whose principles are so profoundly rooted in the real, so strictly dependent upon the very structure of the being they rule, experiences no embarrassment in solving the much-debated problem of the basis of morality. The basis of morality is human nature itself. Moral good is every object, every operation enabling man to achieve the virtualities of his nature and to actualize himself according to the norm of his essence, which is that of a being endowed with reason. Thomistic morality is, accordingly, a naturalism. But it is by that very fact a rationalism because reason acts as its rule. Just as nature makes those beings which are not endowed with reason act according to what they are, so it insists that beings endowed with reason find out what they are so that they may act accordingly. Become what you are is their highest law. Actualize to their ultimate limits the virtualities of the rational being that you are!